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To get those exits, the memslot where KVM_MEM_USERFAULT is being enabled must drop (at least) all of the translations that the bitmap says should generate faults. Today, simply drop all translations for the memslot. Do so with a new arch interface, kvm_arch_userfault_enabled(), which can be specialized in the future by any architecture for which optimizations make sense. Make some changes to kvm_set_memory_region() to support setting KVM_MEM_USERFAULT on KVM_MEM_GUEST_MEMFD memslots, including relaxing the retrictions on guest_memfd memslots from only deletion to no moving. Signed-off-by: James Houghton Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 23 ++++++++++++++++++ include/uapi/linux/kvm.h | 5 +++- virt/kvm/kvm_main.c | 51 ++++++++++++++++++++++++++++++++++++---- 3 files changed, 74 insertions(+), 5 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 9a85500cd5c50..bd5fb5ae10d05 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -597,6 +597,7 @@ struct kvm_memory_slot { unsigned long *dirty_bitmap; struct kvm_arch_memory_slot arch; unsigned long userspace_addr; + unsigned long __user *userfault_bitmap; u32 flags; short id; u16 as_id; @@ -1236,6 +1237,20 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm); void kvm_arch_flush_shadow_memslot(struct kvm *kvm, struct kvm_memory_slot *slot); +#ifndef __KVM_HAVE_ARCH_USERFAULT_ENABLED +static inline void kvm_arch_userfault_enabled(struct kvm *kvm, + struct kvm_memory_slot *slot) +{ + /* + * kvm_arch_userfault_enabled() must ensure that new faults on pages + * marked as userfault will exit to userspace. Dropping all + * translations is sufficient; architectures may choose to optimize + * this. + */ + return kvm_arch_flush_shadow_memslot(kvm, slot); +} +#endif + int kvm_prefetch_pages(struct kvm_memory_slot *slot, gfn_t gfn, struct page **pages, int nr_pages); @@ -2524,6 +2539,14 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu, if (fault->is_private) vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_PRIVATE; } + +bool kvm_do_userfault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault); + +static inline bool kvm_is_userfault_memslot(struct kvm_memory_slot *memslot) +{ + return memslot && memslot->flags & KVM_MEM_USERFAULT; +} + #endif #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index d00b85cb168c3..e3b871506ec85 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -40,7 +40,8 @@ struct kvm_userspace_memory_region2 { __u64 guest_memfd_offset; __u32 guest_memfd; __u32 pad1; - __u64 pad2[14]; + __u64 userfault_bitmap; + __u64 pad2[13]; }; /* @@ -51,6 +52,7 @@ struct kvm_userspace_memory_region2 { #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) #define KVM_MEM_READONLY (1UL << 1) #define KVM_MEM_GUEST_MEMFD (1UL << 2) +#define KVM_MEM_USERFAULT (1UL << 3) /* for KVM_IRQ_LINE */ struct kvm_irq_level { @@ -443,6 +445,7 @@ struct kvm_run { /* KVM_EXIT_MEMORY_FAULT */ struct { #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 3) +#define KVM_MEMORY_EXIT_FLAG_USERFAULT (1ULL << 4) __u64 flags; __u64 gpa; __u64 size; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index eec82775c5bfb..bef6760cd1c0e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1747,6 +1747,14 @@ static void kvm_commit_memory_region(struct kvm *kvm, if (old->dirty_bitmap && !new->dirty_bitmap) kvm_destroy_dirty_bitmap(old); + /* + * If KVM_MEM_USERFAULT is being enabled for the slot, drop the + * translations that are marked as userfault. + */ + if (!(old_flags & KVM_MEM_USERFAULT) && + (new_flags & KVM_MEM_USERFAULT)) + kvm_arch_userfault_enabled(kvm, old); + /* * The final quirk. Free the detached, old slot, but only its * memory, not any metadata. Metadata, including arch specific @@ -2039,6 +2047,12 @@ static int kvm_set_memory_region(struct kvm *kvm, if (id < KVM_USER_MEM_SLOTS && (mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES) return -EINVAL; + if (mem->flags & KVM_MEM_USERFAULT && + ((mem->userfault_bitmap != untagged_addr(mem->userfault_bitmap)) || + !access_ok(u64_to_user_ptr(mem->userfault_bitmap), + DIV_ROUND_UP(mem->memory_size >> PAGE_SHIFT, BITS_PER_LONG) + * sizeof(long)))) + return -EINVAL; slots = __kvm_memslots(kvm, as_id); @@ -2071,14 +2085,15 @@ static int kvm_set_memory_region(struct kvm *kvm, if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages) return -EINVAL; } else { /* Modify an existing slot. */ - /* Private memslots are immutable, they can only be deleted. */ - if (mem->flags & KVM_MEM_GUEST_MEMFD) - return -EINVAL; if ((mem->userspace_addr != old->userspace_addr) || (npages != old->npages) || ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) return -EINVAL; + /* Moving a guest_memfd memslot isn't supported. */ + if (base_gfn != old->base_gfn && mem->flags & KVM_MEM_GUEST_MEMFD) + return -EINVAL; + if (base_gfn != old->base_gfn) change = KVM_MR_MOVE; else if (mem->flags != old->flags) @@ -2102,11 +2117,13 @@ static int kvm_set_memory_region(struct kvm *kvm, new->npages = npages; new->flags = mem->flags; new->userspace_addr = mem->userspace_addr; - if (mem->flags & KVM_MEM_GUEST_MEMFD) { + if (mem->flags & KVM_MEM_GUEST_MEMFD && change == KVM_MR_CREATE) { r = kvm_gmem_bind(kvm, new, mem->guest_memfd, mem->guest_memfd_offset); if (r) goto out; } + if (mem->flags & KVM_MEM_USERFAULT) + new->userfault_bitmap = u64_to_user_ptr(mem->userfault_bitmap); r = kvm_set_memslot(kvm, old, new, change); if (r) @@ -4980,6 +4997,32 @@ static int kvm_vm_ioctl_reset_dirty_pages(struct kvm *kvm) return cleared; } +#ifdef CONFIG_KVM_GENERIC_PAGE_FAULT +bool kvm_do_userfault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) +{ + struct kvm_memory_slot *slot = fault->slot; + unsigned long __user *user_chunk; + unsigned long chunk; + gfn_t offset; + + if (!kvm_is_userfault_memslot(slot)) + return false; + + offset = fault->gfn - slot->base_gfn; + user_chunk = slot->userfault_bitmap + (offset / BITS_PER_LONG); + + if (__get_user(chunk, user_chunk)) + return true; + + if (!test_bit(offset % BITS_PER_LONG, &chunk)) + return false; + + kvm_prepare_memory_fault_exit(vcpu, fault); + vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_USERFAULT; + return true; +} +#endif + int __attribute__((weak)) kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) { -- 2.50.0.rc2.692.g299adb8693-goog